Body Movements

Q48. How does movement occur in the human body?

Ans. Muscles plays very important role in movement. They are the masses of tough, elastic tissue that pull our bones when we move. Together, our bones, muscles, and joints — along with tendons, ligaments, and cartilage enable us to do every day physical activities.

Q49. Differentiate between bone and cartilage.

Ans.

Q50. What do you mean by ‘streamlined’ shape?

Ans. Streamlined body shape is a shape where head and tail are smaller than the middle portion of the body. Such body when travel through a fluid or gaseous medium overcome the friction caused by air and water.

Example - Body of fish is streamlined to move easily through water.

Q51. What makes snakes to move fast on the ground?

Ans. The snake’s body curves into many loops. Each loop of the snake gives it a forward push by pressing against the ground. Since its long body makes many loops and each loop gives it this push, the snake moves forward very fast and not in a straight line.

Q52. What is rib cage? What is the role of rib cage in our body?

Ans. The enclosing structure formed by the ribs and the bones to which they are attached is called ribcage.

Role of rib cage in our body

                       i.        Rib cage encloses and protects the heart and lungs.

                      ii.        It provides a strong framework onto which the muscles of the shoulder girdle, chest, upper abdomen and back can attach.

Q53. Why muscles work in pairs to move a bone?

Ans. Muscles work in pairs. When one of them contracts, the bone is pulled in that direction. The other muscle of the pair relaxes. To move the bone in the opposite direction, the relaxed muscle contracts to pull the bone towards its original position, while the first relaxes. A muscle can only pull. It cannot push. Thus, two muscles have to work together to move a bone.

Q54. How does earthworm move through the soil?

Ans. Earthworm does not have bones. It has muscles which help to extend and shorten the body. During movement, the earthworm first extends the front part of the body, keeping the rear portion fixed to the ground. Then it fixes the front end and releases the rear end. It then shortens the body and pulls the rear end forward. This makes it move forward by a small distance. Repeating such muscle expansions and contractions, the earthworm can move through soil.

Q55. What modifications in the body of the birds help them to fly?

Ans.  The following modifications in the body of the birds help them to fly:

                             i.        Their bones are hollow and light.

                            ii.        The bones of the hind limbs are typical for walking and perching.

                           iii.        Bony parts of the forelimbs are modified as wings.

                           iv.        The shoulder bones are strong.

                            v.        The breastbones are modified to hold muscles of flight which are used to move the wings up and down.

Q56. How does fish move in water?

Ans. The streamlined shape of the fish allows water to flow around it easily and help the fish to move in water. The skeleton of the fish is covered with strong muscles. During swimming, muscles make the front part of the body curve to one side and the tail part swings towards the opposite side. The fish forms a curve. Then, quickly, the body and tail curve to the other side. This makes a jerk and pushes the body forward. A series of such jerks make the fish swim ahead. This is helped by the fins of the tail.